War is hell. And for many soldiers, the experience leaves lasting scars. And not just physical ones. A subset of veterans develop post-traumatic stress disorder, or PTSD. But it might not be only the horrors of battle that make them susceptible. According to a study in the journal Psychological Science [link to come] echoes of childhood abuse may contribute.

Psychologists assessed the mental health of hundreds of Danish soldiers before, during and eight months after they were shipped to Afghanistan. Turns out the vast majority, some 84 percent, were resilient, showing no undue signs of stress at any time. A small number, about 4 percent, developed PTSD, with symptoms that showed up when the troops returned home.

When the researchers compared those two groups, they discovered that the cohort with PTSD had not been exposed to more battlefield trauma—but they were more likely to have experienced violence or abuse in civilian life, particularly as a child.

For the remaining soldiers, being deployed actually helped: something about being part of the team quelled the anxiety they started out with. That finding suggests that PTSD is not uniform, even for those in uniform. And that one man’s poison may be another man’s cure.